Hydrogen-entrained air total consumption aspirator burner



United States Patent Office 3,430,864 Patented Mar. 4, 1969 Filed May26, 1967, Ser. No. 641,523 US. Cl. 239-424 Claims Int. Cl. B0511 7/06ABSTRACT OF THE DISCLOSURE An aspirating burner consisting of a chamberconnected to a single source of pressurized fuel gas, such as hydrogen.The chamber has a top aperture centrally located in a counterbore in thetop of the chamber body. An aspirating tube is supported in a centerpost in the chamber, the top end of the tube extending centrally throughthe top opening and terminating slightly above, defining an annular gasnozzle orifice. The lower end of the tube is received in a vesselcontaining a sample liquid to be spectrometrically analyzed by the flamemethod. The passage of the pressurized fuel gas through the annularnozzle orifice effects aspiration of the sample through the tube andpartially collimates the stream of aspirated liquid forming the flamestructure.

This invention relates to burners, and more particularly to anaspirating burner for use in spectrometrically examining materials bythe flame method.

A main object of the invention is to provide a novel and improvedaspirating burner for use in a flame spectrometer, said burner beingsimple in construction, being convenient to use, and requiring theconnection thereto of only a single source of pressurized gas, therebyminimizing the need for associated gas-control apparatus.

A further object of the invention is to provide an improved aspiratingburner for a flame spectrometer, the burner requiring no internal orexternal adjustments, operating with a minimum of noise, havingdependable aspiration properties, being unlikely to clog, and beingeconomical to operate.

A still further object of the invention is to provide an improvedaspirating burner which is rugged in construction, which is inexpensiveto fabricate, which provides a low background level of flame, which hasa higher flame signal-to-noise ratio for many elements, and more freedomfrom drift, as compared with an oxy-hydrogen burner, and which produceslower spectral interference for certain elements than that present withburners of the prior art.

A still further object of the invention is to provide an improvedaspirating burner which forms a flame with a hydrogen central core, thusretarding refractory oxide formation, which is easy to clean, which iscapable of aspirating sample solution into a flame by only the use of asingle pressurized fuel gas, such as hydrogen, which provides a flamesuitable for sensitive reproducible photometry, and suitable for use inatomic emission, atomic absorption, and atomic fluorescence studies, andwhich is particularly suited for use with atomic fluorescence studiesusing a continuum source, and for analyzing certain metals by thismethod, whereas such metals produce excessive scattering effects whenintroduced into other flames.

A still further object of the invention is to provide an improvedmechanically stabilized aspirating burner ca- 70 Further objects andadvantages of the invention will become apparent from the followingdescription and claims, and from the accompanying drawings, wherein:

FIGURE 1 is a plan diagrammatic view showing a typical flamespectrometer employing an improved aspirating burner constructed inaccordance with the present invention.

FIGURE 2 is an enlarged vertical cross-sectional view takensubstantially on the line 2-2 of FIGURE 1.

FIGURE 3 is a top plan view taken substantially on line 3-3 of FIGURE 2.

FIGURE 4 is an enlarged fragmentary cross-sectional view takensubstantially on line 4-4 of FIGURE 3.

Referring to the drawings, 11 generally designates a flame spectrometeremploying an improved burner constructed in accordance with the presentinvention. The spectrometer 11 is of the type employing a verticallypivoted grating 12 in conjunction with a pair of stationary mirrors 13,14, vertically mounted to define a folded optical path, shown in dottedview in FIGURE 1, between the burner, shown at 15, and a photocell orphotomultiplier tube, shown at 16. The spectrometer includes a suitableslit mechanism 17, provided with an entrance slit assembly 18 and anexit slit assembly 19. The burner 15 is substantially surrounded by asuitable protective burner chimney 20. The various components of thespectrometer, with the exception of the burner 15, are of conventionalconstruction.

The burner 15 is supplied with pressurized fuel gas, for example,hydrogen at a pressure between 4 psi. and 15 psi, from a suitable sourcethrough a conduit 21 provided with a needle valve 22 and a pressuregauge 23. Conduit 21 is connected to the inlet conduit 24 of burner 15by a short length of flexible tubing, shown at 25.

Referring now to FIGURES 2, 3 and 4, it will be seen that the burner 15comprises a base member 26, which may be hexagonal, or of any othersuitable shape, integrally formed with an upstanding externally threadedstud portion 27 and a reduced upstanding central hollow post portion 28in which is coaxially secured a hypodermic tube 29. A gas chamber 30,which may also be of hexagonal external shape, is threadedly secured onthe stud portion 27 and is sealed relative to base member 26 by theprovision of a resilient deformable O-ring 31 in a downwardly facingannular groove 32 formed in the bottom rim of chamber 30.

The gas inlet conduit 24 is connected to the chamber 30 at the lowerportion of the interior space 33 of said chamber. The top end of chamber30 is formed with the frusto-conical, upwardly tapering burner tip 34,with the inside of the tip having a frusto-conical cavity 35. Thehypodermic tube 29 projects upwardly from the top end of post member 28centrally through a circular aperture 36. The top portion of tip 34 isformed with a cylindrical center counterbore 37, with the aperture 36located accurately at the center of the bottom wall of the counterbore.Tube 29 terminates a short distance d, of the order of between 0.0005in. and 0.0025 in., above the top plane of aperture 36. The aperture 36is dimensioned to provide an annular orifice 38 around the top end ofthe tube 29. In accordance with the present invention, the aperture 36is of sufiicient diameter to provide an annular orifice of approximately0.0025 inch in radial width. This may be varied within reasonablelimits. The size of the cylindrical counterbore 37 is quite critical inrelation to the size of the annular orifice 38. In a preferred form ofthe invention, the counterbore height is approximately equal to itsdiameter, and the counterbore diameter is approximately four times theoutside diameter of the annular orifice 38. Thus, in a typical design,the following dimensional values were employed:

The tube 29 must be accurately concentric (within about 0.0005 inch)with relation to aperture 36. The concentricity of said tube ismaintained by supporting it in the upstanding relatively thick rigidpost member 28, which extends substantially to the bottom plane of theburner tip cavity 35, so that only a short length of the tube 29 extendsupwardly from the top end of post member 28.

In operation, the burner is mounted with the lower end of tube 29immersed in a quantity of sample liquid 39 contained in a suitablereceptacle 40 positioned below the burner. The fuel gas, for example,hydrogen, is admitted into the burner cavity 33 at a pressure between 4psi. and 15 p.s.i. The fuel gas passes through the annular orifice 38into the cylindrical counterbore 37, above which combustion takes place.The release of the pressurized fuel gas through the annular restriction38 with resultant venturi effect generates a low pressure region in thebottom of the counterbore which causes aspiration of the liquid sampleup through the tube 29 and discharge thereof into the burning fuel gasand entrained atmospheric air above the tip 34.

The discharge of the aspirant-fuel gas mixture into the bottom of thecylindrical enclosure 37, open at its top end, has the effect ofincreasing the aspiration rate, due to contouring of the fiow streamlines, and also has the effect of partially collimating the stream ofaspirated liquid.

In the typical design above described, it was found that the minimumfuel gas pressure to provide adequate aspiration was about 4 p.s.i. Themaximum fuel gas pressure to provide a proper spectrographic flame wasabout 15 p.s.i. The fuel flow rate was approximately 7.5 liters perminute.

Other fuel gases may be employed, with suitable dimentional changes inthe burner. Among such other gases possibily capable of use are methane,ethane, acetylene or LPG. In all cases, the oxidant consists ofentrained air which mixes with the fuel gas after it leaves the burner.

Because of the fact that the concentricity of the tube 29 and annularorifice 38 is rather critical, the supporting post 28 should be ofsufiicient length so that not more than about /s inch of tube 29 extendspast the upper end of the post. If the burner is properly aligned duringassembly, no further alignment is necessary during the life of theburner.

While a specific embodiment of a burner for use in a flame spectrometerhas been disclosed in the foregoing description, it will be understoodthat various modifications within the spirit of the invention will occurto those skilled in the art. Therefore it is intended that nolimitations be placed on the invention except as defined by the scope ofthe appended claims.

What is claimed is:

1. In a flame spectrometer, a source of pressurized fuel gas, a burnerchamber connected to said source, said burner chamber having a burnertip at its top end, said tip being formed with a counterbore and with anaperture located substantially centrally in the bottom of saidcounterbore, and an aspirating tube mounted substantially centrally 1nsaid burner chamber, the top end of the aspirating tube extendingcentrally through said aperture and terminating a relatively shortdistance above the aperture, defining an annular relatively restrictedgas nozzle orifice between the aspirating tube and the aperture.

2. The structural combination of claim 1, and wherein the annularorifice has a radial width of between 0.002 inch and 0.003 inch and theaperture has a diameter approximately one fourth that of thecounterbore.

3. The structural combination of claim 2, and wherein the pressure ofthe fuel gas is between 4 pounds per square inch and 15 pounds persquare inch.

4. The structural combination of claim 3, and wherein the fuel gas ishydrogen.

5. The structural combination of claim 4, and wherein the height of thecounterbore is substantially equal to its diameter.

6. The structural combination of claim 2, and wherein the diameter ofthe counterbore is approximately 0.13 inch and the fuel gas compriseshydrogen at a pressure between 4 pounds per square inch and 15 poundsper square inch.

7. The structural combination of claim 1, and a rigid post element inthe chamber closely surrounding and supporting the aspirating tube andterminating a short distance below said aperture.

8. The structural combination of claim 7, and wherein the top end ofsaid post element is spaced approximately one eighth inch below saidaperture.

9. The structural combination of claim 8, and wherein the counterborediameter and height are approximately equal to 0.13 inch, the aperturehas a diameter approximately one fourth that of the counterbore, theannular orifice has a radial width of between 0.002 inch and 0.003 inch,and the fuel gas comprises hydrogen at a pressure between 4 pounds persquare inch and 15 pounds per square inch.

10. The structural combination of claim 9, and wherein the interior ofthe tip tapers upwardly in shape substantially from the top end of saidpost element up to said aperture.

References Cited UNITED STATES PATENTS 2,379,161 6/ 1945 Krops 2394242,532,687 12/ 1950 Weichselbaum.

2,562,874 7/1951 Weichselbaum 239424 2,714,833 8/ 1955 Gilbert.

2,858,729 11/1958 Keyes.

2,912,064 11/ 1959 Friedell 239-424 EVERETT W. KIRBY, Primary Examiner.

US. Cl. X.R.

